Handle the return values of realtime updates and stores more accurately.

Handle the return values of realtime updates and stores more accurately.

Realtime backends' update and store callbacks return the number of rows affected,
or -1 if there was a failure. There were a couple of issues:

* The config API was treating 0 as a successful return, and positive values as
  a failure. Now the config API treats anything >= 0 as a success.

* res_sorcery_realtime was treating 0 as a successful return from the store
  procedure, and any positive values as a failure. Now sorcery treats anything
  > 0 as a success. It still considers 0 a "failure" since there is no change
  to report to observers.

Review: https://reviewboard.asterisk.org/r/3341

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/12@410592 65c4cc65-6c06-0410-ace0-fbb531ad65f3